1. Field of the Invention
This invention relates to low sulfur gas oils derived from petroleum distillation fractions, and more particularly to low sulfur gas oils suitable for use as a diesel oil.
2. Description of the Prior Art
Currently, diesel gas oils have been produced by mixing a desulfurized gas oil base obtained by treating a straight gas oil using a conventional desulfurization reaction apparatus, with base materials or gas oil fractions. Such base materials are those produced by hydrocracking a heavy oil. Such gas oil fractions are those produced by thermal cracking or catalytic cracking a heavy oil. On the circumstances, the base material are those obtained by hydro-refining such gas oil fractions. In this connection, there are two choices to reduce the sulfur concentration of a final gas oil. One is to reduce the sulfur concentration of each base materials. The other is to produce a base material of an extremely low sulfur concentration and then to mix it with another base material to an extent of allowable sulfur concentration.
However, recent issues concerning with the environment have required reducing the amounts of NOx and particulates contained in the exhaust gas of diesel engine automobiles. In many foreign countries, there are some movements regarding a regulation emphasizing to decrease the sulfur concentration of diesel gas oils. Specifically, the regulation requires gradually bringing down the sulfur concentration of a diesel oil from 500 ppm which is currently accepted, to 350 ppm and to 50 ppm in the feature. However, conventional methods are limited to produce a diesel gas oil having a sulfur concentration of 500 ppm.
An object of the present invention is to provide a low sulfur diesel gas oil of less than 350 ppm or below, furthermore 50 ppm or below in sulfur concentration causing the formation of particulates in the exhaust gas of a diesel engine automobile.
It has now been found after an extensive research and study that the expected low sulfur gas oil can be produced by using one or more gas oil bases obtained by hydrogenating some specific fractions of petroleum distillations under the certain conditions or alternatively by mixing one or more of these gas oil bases with a small amount of straight kerosene or gas oil.
According to one aspect of the present invention, there is provided with a low sulfur gas oil at least 90% of total volume which consists of one or more gas oil bases (a) to (d) below and the sulfur concentration of which is no greater than 350 ppm:
(a) a gas oil base produced by hydrodesulfurizating a fraction obtained from an atmospheric pressure distillation column and having a 5% recovered temperature in the range of 140 to 310.degree. C. and a 90% recovered temperature of lower than 340.degree. C., under reaction conditions with a hydrogen partial pressure of 20 to 70 kg/cm.sup.2, an LHSV (liquid hourly space velocity) of 1.0 to 20.0 and a reaction temperature of 280 to 450.degree. C.; PA1 (b) a gas oil base produced by hydrodesulfurizating a fraction obtained from an atmospheric pressure distillation column and having a 5% recovered temperature in the range of 140 to 340.degree. C. and a 90% recovered temperature of lower than 340 to 380.degree. C., under reaction conditions with a hydrogen partial pressure of 20 to 150 kg/cm.sup.2, an LHSV of 0.1 to 10.0 and a reaction temperature of 330 to 450.degree. C.; PA1 (c) a gas oil base having an initial boiling point of 260.degree. C. or higher and a 90% recovered temperature of 345.degree. C. or below and obtained from fractions produced by hydrocracking a fraction obtained from an atmospheric distillation column and having an initial boiling point of 260.degree. C. or higher and/or a vacuum gas oil obtained from a vacuum distillation column, under reaction conditions with a hydrogen partial pressure of 30 to 100 kg/cm.sup.2, an LHSV of 0.1 to 10.0 and a reaction temperature of 330 to 450.degree. C.; and PA1 (d) a gas oil base having an initial boiling point of 260.degree. C. or higher and a 90% recovered temperature of 365.degree. C. or below and obtained from fractions produced by hydrocracking a fraction obtained from an atmospheric distillation column and having an initial boiling point of 260.degree. C. or higher in and/or a vacuum gas oil obtained from a vacuum distillation column, under reaction conditions with a hydrogen partial pressure of 100 to 250 kg/cm.sup.2, an LHSV of 0.1 to 10.0 and a reaction temperature of 350 to 450.degree. C.
According to the other aspect of the present invention, there is provided a low sulfur gas oil the total volume of which consists of one or more of the above-described gas oil basses (a) to (d) and the sulfur content of which is no greater than 50 ppm.